Issue link: http://read.dmtmag.com/i/34501
COST ANALYSIS Each fleet operation is different, but there is one consistent goal and that is to achieve the best possible operating cost. This section is designed to provide a guide to determining a Cost Per Mile (CPM). The simplest CPM is found by dividing the price of the tire and any retread by the total mileage. While this is an easy calculation, it is very misleading by ignoring many of the added benefits of the tire or the transfer of residual casing value from one life to another. Determining CPM by wheel position could provide an important gauge for performance since each wheel position is a very special case with unique operating requirements. Here are some of the key elements that need to be considered in any analysis: 1. Total mileage (considers new and retread mileage for steer, drive, and trailer) 2. Residual casing values or casing resale value 3. Requirements of the specific wheel position (steer, drive, and trailer) 4. Repairability (dollars spent on additional mounts and dismounts, repair time and labor) 5. Retreadability (additional casing purchases) 6. Fuel efficiency (see section below) 7. Total expected casing life 8. Labor (scheduled and unscheduled) 9. Road call (by shop personnel as well as Emergency calls) 10. Disposal fees 11. Liability Insurance An estimate of the CPM obtained by different tires in different wheel positions is shown in the examples below. STEER AXLE a. MICHELIN ® XZA3 New Tire Price (estimated) ® b. Residual Casing Value (estimated) c. Total Miles (estimated) d. CPM DRIVE AXLE a. MICHELIN ® ® b. Residual Casing Value (estimated) c. Total Miles (estimated) d. CPM YOUR OPERATION a. New Tire Price b. Residual Casing Value c. Total Miles d. CPM $350.00 - $60.00 ÷ 120,000 = $ 0.00241 per mile XDA3 New Tire Price (estimate) $350.00 - $60.00 ÷ 250,000 = $ 0.00116 per mile $ ___________________ - ___________________ ÷ = ___________________ SIX CRITICAL FUNDAMENTALS THAT COST MONEY LOW AIR PRESSURE This is the number one (along with improper alignment) tire maintenance issue in the industry. The goal is to maintain a recommended fleet target pressure based on the application and vary no more than ± 10 psi. Outside of this range, casing fatigue and irregular wear could cost in the range of $15 to $30 on a $300 tire. VALVE CAPS Slow air loss is the primary result of missing or faulty valve caps. Properly installed and maintained valve caps function as a secondary air seal and means to keep debris away from the valve core. Always install a new metal valve cap containing a rubber or plastic seal. Consider a flow- through type system to improve your maintenance program. The resulting annual expense from missing valve caps/air loss may result in $5 to $15 per occurrence. DUAL MISMATCHED AIR PRESSURE The goal is to maintain tires in dual with equal pressure and within the target range of ± 10 psi. Mismatched pressures can cause a permanent irregular wear pattern to develop and, within just a matter of weeks, can potentially be a cause of early tire removal. The matched tire will also be affected by this difference. Based on a loss of 5 to 20% of tread life, a $30 cost may be associated with this situation. 124 Section Nine: Appendix DUAL MISMATCHED HEIGHT The best method of avoiding damage due to having tires of unequal circumferences is to inspect and match tires so that within the dual position, the average diameter difference is no more than 1⁄4 inch. Additionally, tires on axles and axle ends should fall within this guideline to avoid potential damage to the vehicle transmission. Based on a loss of 5 to 20% of treadlife, a $30 cost may be associated with this situation. OVERINFLATION Again, the goal is to maintain a recommended fleet target pressure based on the application and vary no more than ± 10 psi. Overinflated tires are more likely to be damaged by impact breaks and accelerated wear costing from 7 to 15% of life. A cost factor in a range of $15 to $30 could be associated with overinflation. IRREGULAR WEAR Proper air pressure maintenance and a total vehicle alignment program can eliminate most irregular wear. An occurrence of irregular wear, on average, is associated with a 12% loss of tread life, or $15 to $36. It is also not uncommon for irregular wear to cause a loss of up to 50% of usable tread, resulting in a much higher cost.